Police authorities across Europe stepped up security amid fears the demonstrations will become violent.

Turkish police were also placed on alert at airports and tourist resorts, and security was tightened at embassies.

The Turkey Justice Ministry has told all prisons to tighten precautions against possible uprisings, as hundreds of members of the PKK (Kurdistan Workers' Party) are currently serving terms in Turkish prisons.

Although Turkey has not put a convicted prisoner to death since 1984, there is widespread support in the country for Ocalan's execution.